A user may have a disability which introduces challenges in his or her interaction with touch-sensitive input devices. For example, the user's hands may shake in an incontrollable manner. This makes it difficult for the user to perform conventional operations using touch-sensitive input devices, such as drag-and-drop. For instance, in the course of dragging an object, the user may inadvertently lift his or her hands from a touch-sensitive surface of an input device. That event will prematurely terminate the drag-and-drop operation, requiring the user to reselect the object and begin again. In another case, a user may have a vision impairment which prevents the user from visually discerning the details of a user interface presentation. This makes it difficult for the user to interact with small control features of the user interface presentation.
In other situations, a user may have no permanent disabilities, yet may nevertheless encounter a situation in which there is some obstacle which impedes the user's interaction with a touch-sensitive input device. Here, the user may be said to experience situational disabilities.